16 research outputs found
Characterising molecules for fundamental physics: an accurate spectroscopic model of methyltrioxorhenium derived from new infrared and millimetre-wave measurements
Precise spectroscopic analysis of polyatomic molecules enables many striking
advances in physical chemistry and fundamental physics. We use several new
high-resolution spectroscopic devices to improve our understanding of the
rotational and rovibrational structure of methyltrioxorhenium (MTO), the
achiral parent of a family of large oxorhenium compounds that are ideal
candidate species for a planned measurement of parity violation in chiral
molecules. Using millimetre-wave and infrared spectroscopy in a pulsed
supersonic jet, a cryogenic buffer gas cell, and room temperature absorption
cells, we probe the ground state and the Re=O antisymmetric and symmetric
stretching excited states of both CH3 187 ReO3 and CH3 185 ReO3 isotopologues
in the gas phase with unprecedented precision. By extending the rotational
spectra to the 150-300 GHz range, we characterize the ground state rotational
and hyperfine structure up to J = 43 and K = 41, resulting in refinements to
the rotational, quartic and hyperfine parameters, and the determination of
sextic parameters and a centrifugal distortion correction to the quadrupolar
hyperfine constant. We obtain rovibrational data for temperatures between 6 and
300 K in the 970-1015 cm-1 range, at resolutions down to 8 MHz and accuracies
of 30 MHz. We use these data to determine more precise excited-state
rotational, Coriolis and quartic parameters, as well as the ground-state
centrifugal distortion parameter D K of the 187 Re isotopologue. We also
account for hyperfine structure in the rovibrational transitions and hence
determine the upper state rhenium atom quadrupole coupling constant eQq'
Rotational spectrum and tentative detection of DCOOCH3–Methyl formate in Orion
New centimeter-wave (7–80 GHz) and submillimeter-wave (580–661 GHz) spectra of a deuterated species of
methyl formate (DCOOCH3) have been measured. Transitions with a maximum value of J = 64 and K = 36 have
been assigned and fitted together with previous measurements. The internal rotation of this compound was treated
using the so-called rho axis method. A total of 1703 transitions were fitted using this method. Only 24 parameters
were employed in the final fit, which has an rms deviation of 94.2 kHz. The dipole moment and the nuclear
quadrupole coupling constants of the deuterated specie have also been obtained. This new study has permitted a
tentative detection of DCOOCH3 in Orion with the IRAM 30 m telescope based on the observation of more than
100 spectral features with low blending effects among the 400 lines expected in the observed frequency domain (for
which over 300 are heavily blended with other species). These 100 transitions are above noise and confusion limited
without heavy blending and cannot be assigned to any other species. Moreover, none of the strongest unblended
transitions is missing. The derived source-averaged total column density for DCOOCH3 is 7.8 × 1014 cm−2
and theDCOOCH3/HCOOCH3 column density ratio varies between 0.02 and 0.06 in the different cloud components
of Orion. This value is consistent with the deuteration enhancement found for other species in this cloud
13C—methyl formate : observations of a sample of high mass starforming regions including Orion—KL and spectroscopic characterization
We have surveyed a sample of massive star-forming regions located over a range of distances from the Galactic centre for
methyl formate, HCOOCH3, and its isotopologues H13COOCH3 and HCOO13CH3. The observations were carried out with the
APEX telescope in the frequency range 283.4-287.4 GHz. Based on the APEX observations, we report tentative detections of
the 13C-methyl formate isotopologue HCOO13CH3 towards the following four massive star-forming regions: Sgr B2(N-LMH),
NGC 6334 IRS 1, W51 e2 and G19.61-0.23. In addition, we have used the 1 mm ALMA science verification observations of
Orion-KL and confirm the detection of the 13C-methyl formate species in Orion-KL and image its spatial distribution. Our
analysis shows that the 12C/13C isotope ratio in methyl formate toward Orion-KL Compact Ridge and Hot Core-SW
components (68.4±10.1 and 71.4±7.8, respectively) are, for both the 13C-methyl formate isotopologues, commensurate with the
average 12C/13C ratio of CO derived toward Orion-KL. Likewise, regarding the other sources, our results are consistent with
the 12C/13C in CO. We also report the spectroscopic characterization, which includes a complete partition function, of the
complex H13COOCH3 and HCOO13CH3 species. New spectroscopic data for both isotopomers H13COOCH3 and HCOO13CH3,
presented in this study, has made it possible to measure this fundamentally important isotope ratio in a large organic
molecule for the first time.This work was supported by the National Science Foundation under grant 1008800. We are grateful to the Ministerio de Economia y Competitividad of Spain for the financial support through grant No. FIS2011-28738-C02-02 and to the French Government through grant No. ANR-08-BLAN-0054 and the French PCMI (Programme National de Physique Chimie du Milieu Interstellaire). This paper makes use of the following ALMA data: ADS/JAO. ALMA#2011.0.00009.SV.ALMAis a partnership of ESO (representing its member states), NSF (USA), and NINS (Japan), together with NRC (Canada) and NSC and ASIAA (Taiwan), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO, and NAOJ. C.F. thanks Dahbia Talbi, Eric Herbst, and Anthony Remijan for enlightening discussions. Finally, we thank the anonymous referee for helpful comments
High resolution spectroscopy of methyltrioxorhenium: towards the observation of parity violation in chiral molecules
Originating from the weak interaction, parity violation in chiral molecules
has been considered as a possible origin of the biohomochirality. It was
predicted in 1974 but has never been observed so far. Parity violation should
lead to a very tiny frequency difference in the rovibrational spectra of the
enantiomers of a chiral molecule. We have proposed to observe this predicted
frequency difference using the two photon Ramsey fringes technique on a
supersonic beam. Promising candidates for this experiment are chiral oxorhenium
complexes, which present a large effect, can be synthesized in large quantity
and enantiopure form, and can be seeded in a molecular beam. As a first step
towards our objective, a detailed spectroscopic study of methyltrioxorhenium
(MTO) has been undertaken. It is an ideal test molecule as the achiral parent
molecule of chiral candidates for the parity violation experiment. For the
187Re MTO isotopologue, a combined analysis of Fourier transform microwave and
infrared spectra as well as ultra-high resolution CO2 laser absorption spectra
enabled the assignment of 28 rotational lines and 71 rovibrational lines, some
of them with a resolved hyperfine structure. A set of spectroscopic parameters
in the ground and first excited state, including hyperfine structure constants,
was obtained for the antisymmetric Re=O stretching mode of this molecule. This
result validates the experimental approach to be followed once a chiral
derivative of MTO will be synthesized, and shows the benefit of the combination
of several spectroscopic techniques in different spectral regions, with
different set-ups and resolutions. First high resolution spectra of jet-cooled
MTO, obtained on the set-up being developed for the observation of molecular
parity violation, are shown, which constitutes a major step towards the
targeted objective.Comment: 20 pages, 6 figure
Caractérisation physico-chimique du céto-limonène par spectroscopie micro-onde 2-20 GHz
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Conformational Flexibility of Limonene Oxide Studied By Microwave Spectroscopy
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Competition between inter-and intra-molecular hydrogen bonding: An infrared spectroscopic study of jet-cooled amino-ethanol and its dimer
International audienceThe Fourier transform IR vibrational spectra of amino-ethanol (AE) and its dimer have been recorded at room temperature and under jet-cooled conditions over the far and mid infrared ranges (50-4000 cm 1) using the White-type cell and the supersonic jet of the Jet-AILES apparatus at the synchrotron facility SOLEIL. Assignment of the monomer experimental frequencies has been derived from anharmonic frequencies calculated at a hybrid CCSD(T)-F12/MP2 level. Various thermodynamical effects in the supersonic expansion conditions including molar dilution of AE and nature of carrier gas have been used to promote or not the formation of dimers. Four vibrational modes of the observed dimer have been unambiguously assigned using mode-specific scaling factors deduced from the ratio between experimental and computed frequencies for the monomer. The most stable g Gg monomer undergoes strong deformation upon dimerization, leading to a homochiral head to head dimer involving two strong hydrogen bonds
Dimerization equilibrium of infrared spectroscopy and electronic structure calculations
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Dimerization equilibrium of infrared spectroscopy and electronic structure calculations
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